Please help with GMAT quant doubts

[Iridium Flare]

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers

Data Sufficiency:
1) If k not equal to 0, 1 and -1, then is 1/k > 0 ?
i) 1/ (k-1) > 0
ii) 1/ (k+1) > 0
Ans: Only statement (i) is sufficient.

2) Martha bought pencils, some worth 23 cents and some worth 21 cents. How many pencils of price 23 cents did she buy?
i) Martha bought a total of 6 pencils
ii) The total value of pencils is 130cents
Ans: Only statement (ii) is sufficient. ( i thought both statements were needed)

3) Is l x-y l > lxl - lyl ?
i) y < x
ii) xy < 0
Ans: Only statement (ii) is sufficient.

4) Is m + z > 0 ?
i) m-3z > 0
ii) 4z-m > 0
Ans: Both statements are needed to arrive at answer.

5) If n and m are positive integers, what is the remainder when [3 (raised to) 4n+2] + m is divided by 10?
i) n = 2
ii) m = 1
Ans: Statement (ii) alone is sufficient.

Problem Solving:
1) If d is the standard deviation of x, y and z, what is the standard deviation of x+5, y+5 and z+5 ?
Options: d, 3d, 15d, d+5, d+15 ?
Ans: d

2) A certain city with a population of 132,000 is to be divided into voting districts, and no district is to have a population that is more than 10% greater than the population of any other district. What is the minimum possible population that the least populated district could have?
Options: 10700, 10800, 10900, 11000, 11100
Ans: 11000

3) The rate of a certain chemical reaction is directly proportional to the square of the concentration of Chemical A present, and inversely proportional to the concentration of Chemical B. If the concentration of Chemical B is increased be 100% what should be the increase/decrease in the concentration of Chemical A to keep the reaction unchanged?
Ans: 40% increase.

4) Score Intervals:50 - 59 : 2
60 - 69 : 10
70 - 79 : 16
80 - 89 : 27
90 - 99 : 18

Which score interval contains the median of the 73 scores?
Ans: 80-89


Would appreciate the help... Thanks.

[utsavmamoria]

1) If k not equal to 0, 1 and -1, then is 1/k > 0 ?
i) 1/ (k-1) > 0
ii) 1/ (k+1) > 0
Ans: Only statement (i) is sufficient.

The second statement gives
1/ (k+1) > 0 or k+1 > 0 or K >-1

But K can be negative (-1 < k < 0 ) or positive k > 0
so nothing can be concluded

The first statement Gives
1/ (k-1) > 0 or k-1 > 0 or k > 1
In this case , we can conclude that 1/k > 0 .

2) Martha bought pencils, some worth 23 cents and some worth 21 cents. How many pencils of price 23 cents did she buy?
i) Martha bought a total of 6 pencils
ii) The total value of pencils is 130cents
Ans: Only statement (ii) is sufficient. ( i thought both statements were needed)

Only the second statement is sufficient.This is so because the number of pencils bought can only be a whole number.

23x + 21y = 130

The only Possible solution is x = 2 and y = 4

3) Is l x-y l > lxl - lyl ?
i) y < x
ii) xy < 0
Ans: Only statement (ii) is sufficient.

According to the second statement , two conditiones arise

x>0 and y<0
x<0 and y >0

Take any example and you can say that the statement is true.

4) Is m + z > 0 ?
i) m-3z > 0
ii) 4z-m > 0
Ans: Both statements are needed to arrive at answer.

Adding the two statement gives m > 0

The second statement says 4z>m which means Z is a positive number

Therefore only using both statements can we say m + z > 0

5) If n and m are positive integers, what is the remainder when [3 (raised to) 4n+2] + m is divided by 10?
i) n = 2
ii) m = 1
Ans: Statement (ii) alone is sufficient.

3^(4n+2) will always end in 9
So 3^(4n+2) + 1 will always have the last digit as 0 . So reminder is zero

Yenjaay

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers

Data Sufficiency:
1) If k not equal to 0, 1 and -1, then is 1/k > 0 ?
i) 1/ (k-1) > 0
ii) 1/ (k+1) > 0
Ans: Only statement (i) is sufficient.


Would appreciate the help... Thanks.

for 1/k>0 ===========>k>0
1/k-1>0============>k-1>0====>k>0

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers


2) Martha bought pencils, some worth 23 cents and some worth 21 cents. How many pencils of price 23 cents did she buy?
i) Martha bought a total of 6 pencils
ii) The total value of pencils is 130cents
Ans: Only statement (ii) is sufficient. ( i thought both statements were needed)



Would appreciate the help... Thanks.

Maximum possible pencils according to statement 2 is 130/21 =6
minimum possible 130/23=6 (since whole 130 has to be used)
So statement 1 is irrelevant
21*6=126
21*4+23*2 is the only possible solution from statement 2 only

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers


3) Is l x-y l > lxl - lyl ?
i) y < x
ii) xy < 0
Ans: Only statement (ii) is sufficient.

Would appreciate the help... Thanks.

Statement 2 gives that x and y are having opposite signs which makes |x-y| becomes |x|+|y| which ia always greater than |xl - lyl

Y<x doesn't lead to anything

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,


4) Is m + z > 0 ?
i) m-3z > 0
ii) 4z-m > 0
Ans: Both statements are needed to arrive at answer.



Would appreciate the help... Thanks.

adding both m get canceled and we get z>0
Then from statement 1 we get m>3z>0

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers

5) If n and m are positive integers, what is the remainder when [3 (raised to) 4n+2] + m is divided by 10?
i) n = 2
ii) m = 1
Ans: Statement (ii) alone is sufficient.



Would appreciate the help... Thanks.

3^4%10=1
So n is not required as the reminder of first term is always (9+m)%10 will give the result

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers


Problem Solving:
1) If d is the standard deviation of x, y and z, what is the standard deviation of x+5, y+5 and z+5 ?
Options: d, 3d, 15d, d+5, d+15 ?
Ans: d


Would appreciate the help... Thanks.

Adding 5 with all terms will not change any terms (number of terms is same and deviation from mean is same even if the the terms and deviation are changing.
[IMG]file:///C:/DOCUME%7E1/vbibin/LOCALS%7E1/Temp/moz-screenshot.jpg[/IMG]

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers


2) A certain city with a population of 132,000 is to be divided into voting districts, and no district is to have a population that is more than 10% greater than the population of any other district. What is the minimum possible population that the least populated district could have?
Options: 10700, 10800, 10900, 11000, 11100
Ans: 11000



Would appreciate the help... Thanks.

sorry i believe that number of districts has to be there

[bibinvarghese]

Originally Posted by Iridium Flare

Hi people,

Need some help with the following sums i found on Kaplan mock papers. I'v given the answers along with the sums... I cant arrive at the answers


3) The rate of a certain chemical reaction is directly proportional to the square of the concentration of Chemical A present, and inversely proportional to the concentration of Chemical B. If the concentration of Chemical B is increased be 100% what should be the increase/decrease in the concentration of Chemical A to keep the reaction unchanged?
Ans: 40% increase.



Would appreciate the help... Thanks.

the rate of reaction is decreased to half so the chemical A has to double the rate for the amount of A has to root of 2=1.414
so an increase of 41.4% has to be there.